Classifications

• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/52—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
  • C02F1/5281—Installations for water purification using chemical agents
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D21/00—Separation of suspended solid particles from liquids by sedimentation
  • B01D21/0018—Separation of suspended solid particles from liquids by sedimentation provided with a pump mounted in or on a settling tank
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D21/00—Separation of suspended solid particles from liquids by sedimentation
  • B01D21/003—Sedimentation tanks provided with a plurality of compartments separated by a partition wall
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D21/00—Separation of suspended solid particles from liquids by sedimentation
  • B01D21/02—Settling tanks with single outlets for the separated liquid
  • B01D21/08—Settling tanks with single outlets for the separated liquid provided with flocculating compartments
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D21/00—Separation of suspended solid particles from liquids by sedimentation
  • B01D21/24—Feed or discharge mechanisms for settling tanks
  • B01D21/2488—Feed or discharge mechanisms for settling tanks bringing about a partial recirculation of the liquid, e.g. for introducing chemical aids
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/52—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2221/00—Applications of separation devices
  • B01D2221/02—Small separation devices for domestic application, e.g. for canteens, industrial kitchen, washing machines
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2305/00—Use of specific compounds during water treatment
  • C02F2305/12—Inert solids used as ballast for improving sedimentation

Definitions

• the present invention relates to a physicochemical treatment process for effluents, in particular surface water intended for consumption.
• coagulation step of neutralizing colloids with a metal salt, a trivalent compound of iron or aluminum in general, to form a microfioc. This coagulation step can be carried out in one or more steps; - flocculation: agglomeration and growth stage of the microfioc.
• This agglomeration step is carried out by the addition of a polyelectrolyte (or polymer), downstream from the coagulation step; decantation: step of separation of the floc and the interstitial water, leading to the production of sludge on the one hand, and clarified water, on the other hand.
• a polyelectrolyte or polymer
• decantation step of separation of the floc and the interstitial water, leading to the production of sludge on the one hand, and clarified water, on the other hand.
• fine weights such as microsand: an example of the implementation of this technique is described in FR-P-1 411 792 and in FR-A-2627704.
• the present invention relates to improvements made to decanted sludge devices and recirculated, these improvements being such that said devices, while retaining their specificities and their advantages, operate at much higher decantation speeds.
• the contact mass in the flocculation reactor B consists of the recirculation of part of the sludge settled at C, this part of recycled sludge being introduced into the flocculator B by l 'through the line 16 and the recirculation pump 18.
• the flow of recirculated sludge represents between 0.5 and 4% of the treated flow.
• the recirculated sludge, the raw water and the polyelectrolyte are brought into contact in a zone of strong turbulence, the polymer as seen in this figure 1 is generally injected in the vicinity of the propeller 10 of the flocculator B.
• the sludge excess concentrates are extracted and discharged.
• the mass of sludge due to recirculation is very high compared to the suspended matter provided by the raw water.
• the system is insensitive to both drops and significant increases in suspended solids of raw water;
• the contact mass offers a specific surface or a very significant spatial occupation, because of its expanded structure, of its low relative density; for example, 1 gram of flocculated sludge in a liter (average concentration in the reactor) occupies, after settling for approximately 5 minutes, a volume equal to 100 ml.
• This very large specific surface or spatial occupation considerably increases the probability of contact between the flocs and very fine particles, coagulated colloids, microorganisms and therefore the probability of "trapping" these suspended matter with great efficiency;
• the speeds announced through the lamellar modules of the decanter are between 10 and 25 m 3 / m 2 .h, which corresponds to decantation speeds UD (flow / surface ratio of the raft decanter) from 6 to 15 m / h.
• decantation speeds UD flow / surface ratio of the raft decanter
• Fml limit mass flow of the flocculated suspension expressed in kg of suspended matter passing through m 2 of decanter base and per hour (kg / m 2 / h).
• the lamellar settling tank is effective as a finisher but it is unable to retain a bed of mud.
• the limiting mass flow is generally less than or close to 20 kg / m 3 .h.
• the CR concentration required for good flocculation is approximately 1 kg / m 3 .
• the settling speed limit Udl is then 20m / h. hence the speed UD applied to the decanter less than 15 m./h. For safety reasons.
• tests are carried out representative of the filterability of the decanted water.
• One of the tests thus usable consists in measuring the time necessary to filter 250 cm 3 of decanted water on a membrane of 5 ⁇ m and under a vacuum of 8.10 4 Pa. The filtration of the water will be all the easier as this time will be short. In the case of a settling tank operating with a settling speed UD equal to 15 m / h, the filterability is approximately 30 seconds.
• the present invention proposes to improve the technique described above with a view to increasing the decantation rates, without affecting the filterability of the decanted water.
• the subject of the present invention is a process for the physico-chemical treatment of effluents, in particular surface water intended for consumption, comprising the successive stages of coagulation, flocculation and decantation, a contact mass being introduced into the water from the coagulation step, therefore during the flocculation step, this contact mass consisting of a portion of the densified sludge from the decantation step and recycled in the flocculation step, this process being characterized in that at least part of the polyelectrolyte ensuring flocculation is injected into the sludge recirculation circuit.
• the method which is the subject of this invention and as defined above can be implemented with a flocculation step using a ballast as contact mass.
• the contact mass is obtained by the addition, upstream of a flocculator, of a new ballast or recycled after cleaning.
• the means for separating and regenerating the ballast to be recycled in the flocculator are means well known to those skilled in the art and under these conditions, they will not be described.
• the ballast generally consists of sand and the continuous extractions relate to approximately 5% of the water flow treated by the decanter; these extractions, loaded with sludge coating the micro sand, must be treated in order to regenerate said sand; the cleaned sand is subsequently reinjected upstream of the flocculator, at the head of the installation.
• the residue generated by this cleaning of the ballast sand represents the excess sludge.
• ballast devices described in the literature and in particular in FR-P-1 411 792 and in FR-A-2 627 704, include recycling of the ballast for obvious reasons of operating cost. Furthermore, in all the documents describing this technology, it is specified that the ballast is always "cleaned”, that is to say regenerated. Indeed, the ballast, "glued” by the polymer, must have the maximum adhesion surface for the precipitation flocs produced chemically during coagulation. Effective physical cleaning is therefore essential to free up the maximum surface area for attachment. Ballast is often sand, with a diameter generally between 50 ⁇ m and 150 ⁇ m, generally called micro-sand.
• the advantage of this flocculation technique with contact mass consisting of a fine ballast lies essentially in the settling speed, which can be 20% to 200% greater, compared to the speeds obtained by the flocculation processes. with contact mass consisting of decanted and recirculated sludge.
• the speeds announced through the lamellar modules are between 25 and 50 m3 / m2.h while the equipment implementing the flocculation process using mud as contact mass is limited. at speeds between about 15 and 30 m3 / m2.h.
• the ballast offers a much smaller contact surface area or percentage of space occupation than mud.
• the concentration in the reactor is approximately 1 g / l and the volume occupied by the sludge after five minutes of settling is approximately 10% of the initial volume;
• ballast concentration in the reactor must reach at least 5 g / l, while the volume occupied by the mud after five minutes of settling does not is only about 1% of the original volume;
• the system is sensitive to pollution spikes due to the lack of availability of attachment sites on the ballast (limitation of the contact mass to 5, 10 g / l maximum).
• this concentration is at least 10 times lower than that measured on devices with mass sludge contact, and frequently involve the installation of additional equipment, downstream of the settling tank, for thickening the extracted sludge.
• the present holder proposes to combine! J process as defined above with flocculation with ballast, while eliminating the drawbacks and limits of the conventional processes recalled above, this process making it possible to obtain settling at high speed.
• this invention relates to a physicochemical treatment process for effluents, in particular surface water intended for consumption, comprising the successive stages of coagulation, flocculation and decantation, characterized in that, during the flocculation step, a ballast is introduced into the sludge whose function consists in making the latter heavier, in that the contact mass used during this flocculation step consists of a portion of the densified sludge coming from the decantation step and recycled continuously in the flocculation step, without washing operation, and in that one injects into the sludge recirculation circuit, at least part of the polyelectrolyte ensuring flocculation.
• ballast is used, used in a different manner from that of the process known as “flocculation with ballast” described above.
• the ballast plays only one role, that of weighting-up and the flocculation function of the contact mass is carried out by the only recirculated sludge.
• the ballast no longer constitutes an adhesion surface offered to the particles but it simply constitutes a weighting device which is incorporated into the recirculated sludge towards the flocculation reactor, this recirculated sludge constituting the contact mass.
• the ballast consists of a material having a particle size between 50 and 500 ⁇ m, preferably between 100 and 300 ⁇ m.
• this ballast is a dense mineral material (real specific mass of particle between 2 and 8 g / ml), in particular sand, garnet or magnetite.
• the excess densified, non-recycled sludge can be rejected without treatment or else it can be treated in order to recover the ballast, this treatment not comprising any thorough cleaning of the ballast separated from the sludge.
• the densified sludge has a better ability to settle.
• the recovery of the ballast is preferably carried out by gravity settling, either inside or outside the settling tank, the recovered ballast then being recycled in the flocculation step.
• FIG. 1 is a schematic view illustrating the principle of the known method described above for physico-chemical treatment in which the contact mass used during the flocculation step consists of decanted and recirculated sludge
• FIG. 2 is a block diagram, similar to FIG. 1 illustrating the process which is the subject of the present invention, with double injection of polyelectrolyte and,
• FIG. 3 illustrates the second aspect of the invention combining the double injection of polyelectrolyte and the addition of ballast.
• the contact mass in the flocculator B consists of a continuous recirculation of part of the densified sludge, after settling and thickening in the settling tank C.
• the part of sludge thus recycled is recirculated to the flocculator B using the recirculation line 16, opening at 14 into the flocculator and to the pump 18.
• the recirculated flow represents between 0.5% and 4% of the treated flow.
• At least part (polymer 2) of the polyelectrolyte necessary for flocculation is introduced into the sludge recirculation circuit 16.
• the possibly remaining part of the polyelectrolyte (polymer 1) is introduced into the flocculation reactor B.
• this introduction of at least part of the polyelectrolyte into the recirculated sludges can be carried out upstream or in downstream of the recirculation pump 18. Generally, this injection will be carried out upstream of the pump 18 so that the mixture of recycled sludge + polyelectrolytes benefits from the mixing of the pump.
• the part of the polyelectrolyte introduced into the recycled sludge can be mixed with the latter in a specific stirred reactor, placed on the recirculation line 16.
• polymer 1 the primary injection of polyelectrolyte (polymer 1) can take place in the flocculation reactor B, in the vicinity of the propeller 10 of the latter as illustrated in FIG. 2, but it can also be carried out in the pipe 12 for supplying the water to be treated into the flocculator (agitated area), upstream or downstream of the intake point 14 of the recirculated sludge via the pipe 16.
• the ratio between the dose of polyelectrolyte introduced into the flocculation reactor B (primary injection) and the dose injected into the sludge recirculation circuit 16 (secondary injection) can vary and be optimized.
• the proportion of polymer injected into the sludge recirculation can vary from 10% to 100% of the total polymer flow, 10% is the dose of polymer necessary to obtain a significant increase in mass flow (greater than 10%). It is possible according to the invention to inject 100% of the polymer into the sludge recirculation circuit. In this case, the mass fluxes are even greater (100 to 200 kg / m 3. ), But the quality of the water deteriorates a little. Indeed, in this case, there is no longer enough free polymer to achieve the bonding between the dense recirculated sludge and the microflocs coming from the coagulation of the raw water.
• the proportion of polymer injected into the sludge recirculation circuit compared to the whole of the polymer injected in the flocculation step, will vary from 10% to 100% with an optimum generally between 20 and 70%.
• an anionic polymer can be injected into the flocculation reactor B and a cationic polymer into recirculated sludge.
• the recirculated sludge can be injected directly into the flocculator B, as illustrated in FIG. 2 or else into line 12 ensuring the connection between the coagulator A and the flocculator B.
• the process which is the subject of the present invention can be applied to any type of water treatment, clarification of water for consumption or industry, treatment of industrial or urban water (primary or tertiary, etc.).
• Tests were carried out on the same test pilot equipped with a coagulator A, a flocculator B and a settling tank C whose settling area SD was equal to 2 m 2 and a sludge recirculation circuit 16 having a recirculation pump 18 of suitable flow.
• the capacity of this test pilot was approximately 100m 3 / h.
• the polyelectrolyte dose was the same in both cases (0.8 g / m 3 ) but slightly higher than usual in order to try to increase the decantation rates UD.
• 100% of the polyelectrolyte was injected into the flocculation reactor B, in the vicinity of its propeller 10 while in the second series of tests, only 50% of the polyelectrolyte was injected in the vicinity of the propeller of 10 and 50% flocculation injected into the sludge recirculation circuit 16. The pilot was adjusted and adjusted so that all other test conditions were otherwise identical.
• the extracted sludge has an improved concentration of around 50%, this result bringing the advantage of making it possible to reduce the size of the sludge treatment systems.
• this third injection point is preferably placed in the transfer line 12 ensuring the connection between the coagulator A and the flocculator B, or in a specific reactor interposed between the coagulator and the flocculator.
• ballast is carried out in the flocculator B.
• the excess sludge can either be purely and simply rejected or treated to recover the ballast.
• the treatment of sludge, for recovery of the sand is different from that of flocculation by ballast (FR-P-1 411 792 and FR-A- 2 627 704).
• the sand is recovered without being cleaned, that is to say without regeneration and the treatment is carried out on concentrated sludge, since it is not necessary to carry out a thorough cleaning sand in the separation phase.
• FIG 3 there is shown schematically in E, the means provided according to the invention to ensure the recovery of ballast.
• the low flow rate of sludge to be extracted 0.1% to 1% of the flow rate of treated water (ie 5 to 50 times lower than in the case of flocculation with ballast) makes it possible to use more sophisticated separation techniques and more efficient, among which we can cite in particular: separation by hydrocyclone, separation by blowing air, separation by elutriation, centrifugal separation, separation by ultrasound,
• the choice of the particle size of this weighting ballast can advantageously be oriented towards larger diameters great.
• This ballast diameter in the process which is the subject of the invention, constitutes a fundamental characteristic for:
• ballast diameter is sufficient, a simple gravity separation, inside or outside the decanter, can be envisaged to allow the ballast to be recovered and recycled.
• the method according to the invention with flocculation with contact mass consisting of densified recirculated sludge has in particular the following advantages: 1. It offers a very high percentage of spatial occupancy of the attachment material, hence a high efficiency of the treatment:
• ballast flocculation eg 250 ⁇ m against ballast flocculation
• the recovered ballast does not need to be cleaned, since there is no attempt to regenerate “clean” sites for coagulation / flocculation. It is therefore possible, and advantageous, to recover the ballast from highly concentrated sludge, a possibility which offers the following advantages:
• the volume of the storage-thickener installed downstream of the settling tank can be reduced in proportion.
• the sand recovery system works on reduced volumes in the same proportions (eg 10 times) and, here again, it is possible to reduce the size of the equipment and the energy consumption.
• the dissociation of the ballast functions - sludge mass for flocculation makes it possible to envisage operating at low flow rate (between less than 20% and 80% of Qmax. Depending on the case) without adding or recirculating the ballast, which allows further reduce operating costs.
• the densification of the sludge obtained by the combination of double injection of polymer and addition of ballast makes it possible to produce decantation equipment at high speed providing spectacular advantages with respect to known installations.
• the variant according to the invention consisting in combining the injection, into the sludge recirculation circuit, of at least part of the polyelectrolyte ensuring flocculation, and the addition of ballast in the flocculator is mainly used in the case of production of flock difficult to densify by the polymer alone or, above all, in the event of an overflow on the installation.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Environmental & Geological Engineering (AREA)
• Life Sciences & Earth Sciences (AREA)
• Hydrology & Water Resources (AREA)
• Engineering & Computer Science (AREA)
• Water Supply & Treatment (AREA)
• Organic Chemistry (AREA)
• General Chemical & Material Sciences (AREA)
• Separation Of Suspended Particles By Flocculating Agents (AREA)
• Treatments Of Macromolecular Shaped Articles (AREA)
• Application Of Or Painting With Fluid Materials (AREA)
• Physical Water Treatments (AREA)
• Catalysts (AREA)
• Biological Treatment Of Waste Water (AREA)

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Citations (7)

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• 1998
  • 1998-01-26 CA CA002279405A patent/CA2279405C/fr not_active Expired - Lifetime
  • 1998-01-26 DE DE69802781T patent/DE69802781T2/de not_active Expired - Lifetime
  • 1998-01-26 PT PT98904219T patent/PT961759E/pt unknown
  • 1998-01-26 AU AU62184/98A patent/AU6218498A/en not_active Abandoned
  • 1998-01-26 DE DE0961759T patent/DE961759T1/de active Pending
  • 1998-01-26 AT AT98904219T patent/ATE210084T1/de active
  • 1998-01-26 EP EP98904219A patent/EP0961759B1/de not_active Expired - Lifetime
  • 1998-01-26 US US09/355,030 patent/US6210588B1/en not_active Expired - Lifetime
  • 1998-01-26 ES ES98904219T patent/ES2138948T3/es not_active Expired - Lifetime
  • 1998-01-26 BR BR9806789-3A patent/BR9806789A/pt not_active IP Right Cessation
  • 1998-01-26 JP JP53168498A patent/JP3945541B2/ja not_active Expired - Fee Related
  • 1998-01-26 WO PCT/FR1998/000134 patent/WO1998032702A1/fr active IP Right Grant
• 1999
  • 1999-07-26 NO NO19993618A patent/NO317246B1/no not_active IP Right Cessation

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